1. Field of the Invention
This invention relates to a structure of a drive section of a power tool. Especially, it relates to improvement of a structure which converts rotational movement of a motor into vibrational movement of an arm with a tool such as a sander.
2. Description of the Prior Art
Conventionally, a structure C as shown in FIG. 5 is known, as a structure of a drive section which converts rotational movement of a motor into vibrational movement of an arm with a tool such as a sander.
The structure C of the drive section has a motor 51 fixed to a housing (not shown). A shaft 53 is fixed to an output shaft 52 of the motor 51. An eccentric section 53a is formed at the tip portion of the shaft 53. The middle portion of the shaft 53 is rotatably supported by a ball bearing 54.
On the other hand, a vibratory arm 55 is vibratably supported by a pin 56. A recess 57 is formed at the back end portion of the vibratory arm 55. The eccentric section 53a is inserted into the recess 57, and thereby the eccentric section 53a is connected to the vibratory arm 55. Both side walls of the recess 57 are formed as contact sections 57a and 57b. The outer circumferential surface (cam surface) of the eccentric section 53a slidably contacts the inside surface of these contact sections 57a and 57b. Moreover, a vibratory member 58 is fixed to the tip portion of the vibratory arm 55. The vibratory member 58 vibrates in the direction as shown by an arrow X in FIG. 5.
FIG. 6 is a sectional view for explaining about operation of each member at the time when rotational movement of the motor 51 is converted into vibrational movement. In addition, FIGS. 6(A1)-6(A4) are views showing a structure of the drive section taken along the line P--P in FIG. 5. FIGS. 6(B1)-6(B4) are plan views of FIGS. 6(A1)-6(A4), respectively. FIG. 6(A1) corresponds to FIG. 6(B1). Hereinbelow, FIGS. 6(A2)-6(A4) correspond to FIGS. 6(B2)-6(B4), respectively.
In FIG. 6, a reference numeral O.sub.1 is a center of the shaft 53. A reference numeral O.sub.2 is a center of the eccentric section 53a.
When the shaft 53 rotates by 90 degrees in the clockwise direction (as shown by an arrow Y in FIG. 6) from the state as shown in FIGS. 6(A1) and 6(B1), the eccentric section 53a also rotates by 90 degrees in the clockwise direction. And, the relationship between the eccentric section 53a and the contact sections 57a, 57b becomes the state as shown in FIGS. 6(A2) and 6(B2). Namely, in the direction of the x axis, the center O.sub.2 moves in the right direction as shown by an arrow Z in FIG. 6(A1), by a distance L between the center O.sub.1 and the center O.sub.2. Thereby, the contact sections 57a and 57b move by the distance L in the right direction along the x axis.
When the shaft 53 further rotates by 90 degrees in the clockwise direction from the state as shown in FIGS. 6(A2) and 6(B2), the relationship between the eccentric section 53a and the contact sections 57a, 57b becomes the state as shown in FIGS. 6(A3) and 6(B3). Thereby, the contact sections 57a and 57b further move by the distance L in the right direction along the x axis.
When the shaft 53 further rotates by 90 degrees in the clockwise direction from the state as shown in FIGS. 6(A3) and 6(B3), the relationship between the eccentric section 53a and the contact sections 57a, 57b becomes the state as shown in FIGS. 6(A4) and 6(B4). Thereby, the contact sections 57a and 57b return by the distance L to the left direction along the x axis.
Furthermore, when the shaft 53 rotates by 90 degrees in the clockwise direction from the state as shown in FIGS. 6(A4) and 6(B4), the relationship between the eccentric section 53a and the contact sections 57a, 57b return to the state as shown in FIGS. 6(A1) and 6(B1). Thereby, the contact sections 57a and 57b further move back by the distance L in the left direction along the x axis.
The operation of the drive section C stated above is repeated. Thereby, the rotational movement of the motor 51 is converted into the vibrational movement of the vibratory arm.
However, there are some problems as follows in the structure of the drive section C stated above.
As shown in FIGS. 6(B1)-6(B4), angle portions D1 and D2 of the eccentric section 53a which abut against the contact surfaces of the contact sections 57a and 57b is formed at a right angle, and the sharp angle portions D1 and D2 slide on the contact surfaces of the contact sections 57a and 57b during swinging motion of the arm 53. For this reason, transfer of power from the motor 51 to the vibratory arm 55 is not performed smoothly. It becomes the cause of generation of vibration and noise. The angle portions D1, D2 and each of contact surfaces of the contact sections 57a, 57b are worn out. For this reason, it becomes the cause of generation of rattling.
The friction between the angle section D1,D2 and the contact surfaces of the contact sections 57a, 57b becomes the cause of producing heat.